Dielectric porcelain material

ABSTRACT

Disclosed are dielectric porcelain materials having compositions falling in the quadrilateral area defined by connecting points A, B, C and D in the ternary diagram of components Al 2  O 3 , CaTiO 3  and SrTiO 3  in the drawing. The points A, B, C and D are represented in mol % as follows: 
     
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     Al 2  O 3   CaTiO 3                                              
                           SiTiO 3                                     
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A      0.99           0.01     0                                          
B      0.96            0.035    0.005                                     
C      0.91           0.04     0.05                                       
D      0.91           0.01      0.08.                                     
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     The dielectric porcelain materials have thermal coefficients between -15 and +15 and a no-load Q not less than 4000.

BACKGROUND OF THE INVENTION

The present invention relates to a dielectric porcelain material used in the micro-wave frequency region. More particularly, the invention relates to such a material used in frequencies higher than X-band, and which effectively demonstrates high no-load Q and stable thermal properties.

ZrO₂ -SnO₂ -TiO₂ and BaO-TiO₂ systems, and those systems partially substituted with other elements, or composite materials having a controlled thermal coefficient obtained by combining positive dielectric porcelains or glass with negative TiO₂, are heretofore well-known. However, their dielectric constants are as high as from 30 to 40. On the other hand, with the increasing use of high frequency regions and from the viewpoint of workability, materials with dielectric constants of about 10, rather than those with high constants as above described, have become of interest in the manufacture of porcelain substrates for dielectric resonators.

Alumina porcelains are known to have small dielectric constants. However, the thermal coefficients of aluminia porcelains which are as high as ±60 ppm/°C. have inhibited their practical applications.

In Japanese Patent Application No. 32113/84, materials are disclosed having compositions falling in the quadrilateral area defined in the Al₂ O₃ -CaO-TiO₂ ternary composition diagram in the application by connecting the following points:

    ______________________________________                                                 Al.sub.2 O.sub.3                                                                            CaO    TiO.sub.2                                          ______________________________________                                         point   A     0.94           0.04 0.02                                                 B     .81            .14  .05                                                  C     .81            .02  .17                                                  D     .94            .01  .05                                          ______________________________________                                    

The materials are manufactured by combining alumina sinterings of thermal coefficients (hereinafter denoted τf) which have negative large-absolute values such as -60 ppm/°C., high no-load Q, small dielectric loss at high frequencies and excellent thermal conductivity, mechanical strength and chemical stability properties, with CaO+TiO₂ -derived calcium-titanate materials of large positive τf values. It has been desired, however, to further improve the τf and no-load Q of the materials which are the invention of Japanese Patent Application No. 32113/84.

The principal object of the present invention is, therefore, to provide a dielectric porcelain material for use in the micro-wave frequency region that has improved τf and no-load Q, and in particular, τf and no-load Q which are improved over those of the materials of Japanese Patent Application No. 32113/84.

SUMMARY OF THE INVENTION

In order to achieve this and other objects of the invention, the CaO and TiO₂ components mixed in the alumina porcelain of the material of Japanese Patent Application No. 32113/84 have been substituted by CaTiO₃ and SrTiO₃, respectively. The composition range of the Al₂ O₃ -CaTiO₃ -SrTiO₃ material of the present invention is restricted to the quadrilateral area defined by the points A, B, C and D in the ternary composition diagram shown in the accompanying drawing.

The sintered porcelain of the present invention contains such minerals as Al₂ O₃, CaTiO₃, SrTiO₃, 6Al₂ O₃.CaO, 16Al₂ O₃.SrO, 6Al₂ O₃.SrO, etc. The Al₂ O₃ contributes toward maintaining high no-load Q, whereas the CaTiO₃, SrTiO₃, and especially stable CaTiO₃, contribute toward the improvement of τf.

BRIEF DESCRIPTION OF THE DRAWINGS

The single FIGURE is a ternary component diagram in which the compositional ranges of Al₂ O₃, CaTiO₃ and SrTiO₃ in the porcelain material according to the present invention are defined.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments are set forth in the following illustrative examples.

EXAMPLE 1 Synthesis of calcium titanate (CaTiO₃)

278 G of calcium carbonate (commercially available CaCO₃ ; reagent grade), 222 g of titanium dioxide (commercially available TiO₂ ; reagent grade), and 800 ml of water were mixed with 2 kg of alumina balls (99.99% pure, 20 mm diameter) in a polyethylene container having a volume of 2 liters under the condition of 84 RPM for 15 hours. The mixture was dried and the product which passed a 60-mesh sieve was calcinated in a 99.99% pure alumina crucible for one hour at 1300° C. using an electric furnace to obtain CaTiO₃. The calcined CaTiO₃ was re-crushed, dried and sieved under the same conditions as described above to obtain CaTiO₃ powder of grains which passed the 60-mesh sieve.

EXAMPLE 2 Synthesis of strontium titanate (SrTiO₃)

324 G of strontium carbonate (commercially available SrCO₃ ; reagent grade), 176 g of titanium dioxide (the same as that used in Example 1) and 800 ml of water were mixed and treated under the same conditions used in the synthesis of CaTiO₃ in Example 1.

EXAMPLE 3 Mixing of the components

The CaTiO₃ and SrTiO₃ powders synthesized in Examples 1 and 2 were appropriately mixed with 1000 kg of commercially available 99.99% pure alumina (average particle size of 0.5μ) to obtain products (Samples 1-22) having compositions as shown in the following Table 1 and in the drawing. The products of Samples 1-12 are indicated at points 1-12 in the drawing. These compositions fall within the quadrilateral area (margins included) defined by points A, B, C and D in the ternary composition diagram shown in the drawing. The products of Samples 13-22 are indicated at points 13-22 in the drawing and these compositions fall outside the said defined quadrilateral area. The compositions represented by points 1, 2, 3, and 4 correspond to the compositions represented by points A, B, C and D, respectively.

Test pieces were prepared in the following manner: For each of Samples 1-22, 1500 ml of water and 5 g of PVA (polyvinyl alcohol) caking agent were added to the appropriate mixture of Al₂ O₃, CaTiO₃ and, when used, SrTiO₃ and the mixture was then mixed with 3 kg of 20 mm diameter 99.99% pure alumina balls in a polyethylene container having a volume of 3 liters under the condition of 84 RPM for 24 hours. The slurried product was pelletized by spray-drying using a 110 mm diameter atomizer at 170° C. and 7200 RPM. The granulated powder was press-formed to obtain cylinders 18.6 mm in diameter and 10.2 mm in length using a metal-mould press with a capacity of 1500 kg/cm². Sinterings 15.5 mm in diameter and 8.5 mm in length were obtained after burning at a temperature of from 1400° to 1500° C. for one hour in an electric furnace. The properties of test pieces 15 mm in diameter and 7 mm in length, obtained after the sinterings were finished by 0.1-s and 0.5-s polishing of the ends and outer surfaces, are shown in the following Table 1.

Also shown in the Table, for reference purposes, are the dielectric constant ε, the thermal coefficient τf and the no-load Q for each of Al₂ O₃, CaTiO₃ and SrTiO₃.

                                      TABLE 1                                      __________________________________________________________________________                               Thermal Coefficient                                  Composition       Dielectric                                                                             of the Resonance                                     (Mole Ratio)      Constant ε                                                                     Frequency τf                                                                         No-load                                    Sample                                                                             Al.sub.2 O.sub.3                                                                    CaTiO.sub.3                                                                         SrTiO.sub.3                                                                        (at 8˜9 GHz)                                                                     (ppmC)    Q    Remarks                               __________________________________________________________________________      1  0.99 0.01 0   10.5    -15       5900 Within                                 2  0.96 0.035                                                                               0.005                                                                              12.2    +13       4200 the                                    3  0.91 0.04 0.05                                                                               13.0    +15       4000 present                                4  0.91 0.01 0.08                                                                               12.8     -8       4000 invention                              5  0.935                                                                               0.04 0.025                                                                              12.6    +14       4100                                        6  0.965                                                                               0.01 0.025                                                                              10.9    -14       4900                                        7  0.935                                                                               0.01 0.055                                                                              11.4    -13       4500                                        8  0.96 0.025                                                                               0.015                                                                              11.6    +0.7      4500                                        9  0.94 0.025                                                                               0.035                                                                              12.0    +1.3      4300                                       10  0.92 0.025                                                                               0.055                                                                              12.4    +2.4      4200                                       11  0.91 0.025                                                                               0.065                                                                              12.5     +3       4100                                       12  0.975                                                                               0.025                                                                               0   11.4    +0.1      5000                                       13  0.955                                                                               0.045                                                                               0   12.6    +20       3800 Outside                               14  0.93 0.045                                                                               0.025                                                                              12.7    +24       3600 the                                   15  0.905                                                                               0.045                                                                               0.05                                                                               13.2    +27       3400 present                               16  0.905                                                                               0.025                                                                               0.07                                                                               12.9    +10       3500 invention                             17  0.905                                                                               0.01 0.085                                                                              13.0     -5       3600                                       18  0.915                                                                               0.005                                                                               0.08                                                                               12.8    -18       3800                                       19  0.935                                                                               0.005                                                                               0.06                                                                               11.0    -19       4300                                       20  0.955                                                                               0.005                                                                               0.04                                                                               10.7    -20       5200                                       21  0.975                                                                               0.005                                                                               0.02                                                                               10.6    -21       5700                                       22  0.995                                                                               0.005                                                                               0   10.1    -22       6000                                           Al.sub.2 O.sub.3                                                                    (99.5%)   9.7    -63       5500                                           CaTiO.sub.3   155     +890      4000                                           SrTiO.sub.3   250     +1640     1100                                       __________________________________________________________________________

For the values shown in Table 1, the measurements of the dielectric constant ε were obtained by the dielectric cylinder resonance method (resonance frequency: 8-9 GHz). The thermal coefficients τf were measured in the temperature range of from 25° to 85° C. and calculated using the following equation:

    τf=-1/2τε-α

wherein τε represents the temperature difference of the dielectric constant, and α represents the coefficient of linear thermal expansion of the porcelain material.

As seen in Table 1, the products according to the present invention have τf values between -15 and +15 and a no-load Q not less than 4000, indicating that they can be effectively used in the micro-wave range, and especially in the frequencies equal to and higher than the X-band.

The present invention has been disclosed in terms of preferred embodiments. The invention, however, is not limited thereto. The scope of the invention is determined by the appended claims and their equivalents. 

What is claimed is:
 1. A dielectric porcelain material having a composition falling in the quadrilateral area defined by connecting points A, B, C and D in the ternary diagram of components Al₂ O₃, CaTiO₃ and SrTiO₃ in the drawing wherein the points A, B, C and D are represented in mol% as follows:

    ______________________________________                                         Al.sub.2 O.sub.3  CaTiO.sub.3                                                                             SrTiO.sub.3                                         ______________________________________                                         A      0.99           0.01     0                                               B      0.96            0.035    0.005                                          C      0.91           0.04     0.05                                            D      0.91           0.01      0.08.                                          ______________________________________                                    


2. The dielectric porcelain material of claim 1 containing minerals selected from Al₂ O₃, CaTiO₃, 6Al₂ O₃.CaO, 16Al₂ O₃.SrO and 6Al₂ O₃.SrO.
 3. The dielectric porcelain material of claim 1 having a thermal coefficient τf between -15 and +15.
 4. The dielectric porcelain material of claim 2 wherein the thermal coefficient τf is measured in the temperature range of from 25° to 85° C. and calculated using the equation:

    τf=-1/2τε-α

wherein τε represents the temperature difference of the dielectric constant and α represents the coefficient of linear thermal expansion of the porcelain material.
 5. The dielectric porcelain material of claim 1 having a no-load Q not less than
 4000. 6. The dielectric porcelain material of claim 1 containing minerals selected from Al₂ O₃, CaTiO₃, 6Al₂ O₃.CaO, 16Al₂ O₃.SrO and 6Al₂ O₃.SrO.
 7. The dielectric porcelain material of claim 1 having a thermal coefficient τf between -15 and +15.
 8. The dielectric porcelain material of claim 6 wherein the thermal coefficient τf is measured in the temperature range of from 25° to 85° C. and calculated using the equation:

    τf=-1/2τε-α

wherein τε represents the temperature difference of the dielectric constant and α represents the linear expansion of the porcelain material.
 9. The dielectric porcelain material of claim 1 having a no-load Q not less than
 4000. 